The objective is to determine the hormones involved in the growth and regression of follicles, corpora lutea and interstitium in the mammalian ova with special reference to hamster and rat. Representative projects include: 1) A single injection of anti-LH serum induces superovulation in the hamster and guinea pig but not in the rat. What is the mechanism of action and what is the explanation for the species difference? What is the effect of anti-L in other species (rabbit, mouse, etc.). 2) A model for inducing atresia in a synchronized population of 30-40 antra follicles has been developed. What are the changes induced by atresia in: steroid levels (in vivo and in vitro), protein synthesis, cyclic AMP and GMP, prostaglandins, vascularity, etc. Can atresia be prevented by various steroids (Silastic implants). 3) What is the explanation for in vitro synthesis of progesterone by hamster ovaries 5 days after hypophysectomy (H)? Is this also true for the H rat in which the corpora lutea persist indefinitely after H? What tissue compartment accounts for the persistence of some steroidogenic activity after H?